Due to the high rate of incidence and the overall mortality, colorectal cancer is one of the most important medical problems modern medicine has to deal with. A lot of research has been done in order to understand the molecular basis of the carcinogenesis process in colorectal adenocarcinoma and now the evolution of the colorectal cancer from normal epithelial cell to cancer cell is one of the best understood models of carcinogenesis. In order to fully understand this process one must have basic knowledge of the histology and the genetics of colorectal adenocarcinoma. Also of great importance is the role that the immune system has to play in the development and progression or regression of this type of cancer – from the basic immune response to the presence of the neoplastic cells, to the immune response that is caused by central necrosis which can lead to stimulation of tumour growth and finally to the immune response that is responsible for the development of cancer in the presence of chronic inflammation. The reason why the biology of the colorectal cancer is so important is that it can not only lead to finding new ways of treatment but mostly because it can lead to a better staging system than the classical Dukes staging system, which in turn can correct under-treatment or over-treatment of colorectal cancer lesions.